Method for preparing gold of high purity

Details Method for preparing gold of high purity Method for preparing gold of high purity

2000-06-16

2001-12-18

King, Roy (Department: 1742)

Specialized metallurgical processes, compositions for use therei

Processes

Free metal or alloy reductant contains magnesium

Reexamination Certificate

active

06331200

ABSTRACT:

The invention relates to a method for preparing gold of high purity from noble metal solutions containing nitrate.
In German Publication: T. Havlik et al.: “The leaching behaviour of tetrahedrite concentrate in nitrate solution” in Metall, 52, 1998, 4, pages 210 to 213, it is disclosed that metals can be dissolved especially well out of nitrate solutions by cementation in the presence of iron ions.
In German Patent 21 54 093 a method has been disclosed, among others, for producing a gold powder from particles of a certain size and shape, which is characterized in that a gold salt solution is reduced at a temperature ranging from 20 to 100° C. with a reducing agent, namely 1) hydroquinone or bromine, chlorine or low alkyl substitution products of hydroquinone or mixtures thereof, or 2) oxalic acid, an alkali salt of oxalic acid or mixtures thereof, or 3) combinations of 1) and 2) in the presence of a protective colloid.
It has long been known to obtain high-purity gold by means of sulfur dioxide from noble metal solutions containing nitrate. A disadvantage of these methods is the necessity of redissolving the products several times. The great number of individual process steps thus called for involves a great amount of time and expense.
From what has been stated, the problem arises of at least partially eliminating the problem by means of a novel process. The problem lies especially in devising a method for producing gold of high purity which succeeds with few working steps.
This problem is solved by the invention by a method according to claim
1
.
In the method of the invention, in a first step the nitrate in the noble metal solution is destroyed, for example by adding a reducing agent to the heated solution. Then the gold ions are reduced to gold by the addition of an acid Fe
2+
solution, the concentration of H
+
in the Fe
2+
solution amounting to at least 4 mol/l. The noble metal solution previously produced free of nitrates has an H
+
ion concentration of 4 mol/l.
It is especially advantageous if the reduction of step b), i.e., the addition of an acid Fe
2+
solution is potential-controlled, since in this manner it is relatively easy to detect the end of the reduction and thus a selective process control is possible.
It is furthermore an advantage if the destruction of t he nitrate is performed with formic acid or ascorbic acid, since these substances specifically reduce nitrate to NO, but not gold ions.
The nitrate destruction is advantageously performed at a temperature of T=+80° C. to +90° C. in order thus to assure an efficient destruction of the nitrate.
Lastly, the solution produced in step a), i.e., the noble metal solution made nitrate-free, is heated before adding the Fe
2+
ion solution to a temperature of T=+60° C., since in this manner the gold is more fine-grained and has fewer inclusions.


REFERENCES:
patent: 21 54 093 C2 (1973-01-01), None
patent: 0073108 (1983-03-01), None
patent: 5222465 (1993-08-01), None
patent: 9272927 (1997-10-01), None
patent: 2120485 (1998-10-01), None
T.Havlik, et al., “The leaching behavior of tetrahedrite concentrate in nitrate solution”, pp. 210-213, dated 1998, No month.

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